Buoyancy Driven Flow
 

Hello sir,
I am modelling natural convection heat transfer between two parallel plates
with Buoyancy using Ansys CFX. up to what value of residual can be acceptable
for Buoyancy Driven Flows(i.e. RMS values for Mass and Momentum,Heat Transfer,Turbulent KE)
Thank You sir

There is no general rule for this. You have to do a sensitivity study where you sweep a range of convergence tolerances and see what effect it has on parameters of interest to you. When you have converged the parameters of interst to you to a tolerance you are happy with then you have found the convergence tolerance you require.